I think we've all thought at one time "Man, if only I could build my own cockpit, then I'd have everything..."
It's a nice fantasy to have, but personally, I don't think I could justify it. In doing some research for the idea (because I really wanted to do it), I found out that those things cost tens and tens of thousands of dollars.
Why?
If you're able to scrape that kind of money together, just put it in a dish and use it for real world flight instruction?
Sure, those are expensive too. And I'm not saying that everyone should do that. But if you've only got the money to do one of the two, why fool around with a pretend airplane, IMHO...